This bike is driving me crazy!!!

[Hans]

Can't really help with the mechanical issues as I know faaarrrk all about 2 strokes, but if you get stuck, I've got a van in Welly, so 021 126 33 65 or 04/ 970 1335. I know it's the wrong thread for this but no-one seems to read the "offering help" thread that much.

[centaurus]

Thanks a lot for the offer Hans. I will try to dismantle the bike this week and have a look around. However, me not having almost any experience repairing bikes and the problem looking quite complicated, chances are I will have to give up and take to a bike shop. If that will be the case, I will use your offer.

Thanks again!

[Hans]

No problem, PM me the day before or something, and we'll take it there.

[Speedracer]

Agree with post #13.
My experience is this:
I bought a kr250 bike which would turn over with a LOT of effort, but it wouldn't idle. (this thing was so far gone I pushed my mate up the road on it to get it to fire). I only paid $300 so I don't really mind.
So yes it would run, with difficulty. It had borderline compression (but still ok according to the manual).
The plugs weren't even that oiled. But it was thicker black oil, not the less viscous 2 stroke oil.

Problem? blown crank case seal.

At a guess:
The high temp from hard riding (or power band) will burn the standard engine oil, but as soon as you idle, it won't get burnt fast enough and will fill up. The leak is also proportional to how hard you ride it, at idle it won't leak much but at high speed it pours in. So when you engine brake, it builds up and gums that cylinder, stopping it firing.

I took the engine completely apart to fix it. Didn't put it back together though

[Nutter34]

Agree with post #13.
My experience is this:
I bought a kr250 bike which would turn over with a LOT of effort, but it wouldn't idle. (this thing was so far gone I pushed my mate up the road on it to get it to fire). I only paid $300 so I don't really mind.
So yes it would run, with difficulty. It had borderline compression (but still ok according to the manual).
The plugs weren't even that oiled. But it was thicker black oil, not the less viscous 2 stroke oil.

Problem? blown crank case seal.

At a guess:
The high temp from hard riding (or power band) will burn the standard engine oil, but as soon as you idle, it won't get burnt fast enough and will fill up. The leak is also proportional to how hard you ride it, at idle it won't leak much but at high speed it pours in. So when you engine brake, it builds up and gums that cylinder, stopping it firing.

I took the engine completely apart to fix it. Didn't put it back together though

Did you notice any gearbox oil usage? That would be a give-away.

[centaurus]

I'm assuming you're talking about the seal between the crank and the gearbox?

I haven't checked the oil level in the gearbox because I don't know how to yet on this bike.

The only thing that puzzles me is the fact that only one exhaust smokes and only one plug gets fowled every time - the one at the low cylinder. The other one looks perfectly normal (it doesn't smoke at all and the plug is perfectly dry). All the possible causes that the guys told me to check, including the crank seal - which I also feel it is the most probable one, should have effect on both cylinders. Right?

[Ixion]

Nope. There'll be another seal between the cylinder crankcase chambers. It's not like a Harley with the conrods both on the same pin. More like a parallel twin.Two conrods, two crankpins. (I think - correction welcome)

[centaurus]

In that case, how would that seal create such an effect? As far as I can tell, having that seal cracked, would make the crank chambers communicate, but both crank chambers should contain fuel mix, right? Having that seal cracked would only produce a lower pressure in the cylinder, but in both cylinders. Correct me if I'm wrong.

[Ixion]

Two seals. One on right , seals crankcase off from primary gearcase. If that leaks oil can enter the crankcase.

One of left, between cranks, seals crankcases off from each other.That doesn't leak (luckily - thats a BAD thing to happen).

There's another one on the non drive side too, but as theres usually no oil on that side the effect is not so noticeable. Odds are if right outer is stuffed, left outer will be also.

Very common on two strokes. Do a site search been a few other people had similar problems.

[Nutter34]

I'm assuming you're talking about the seal between the crank and the gearbox?

I haven't checked the oil level in the gearbox because I don't know how to yet on this bike.

The only thing that puzzles me is the fact that only one exhaust smokes and only one plug gets fowled every time - the one at the low cylinder. The other one looks perfectly normal (it doesn't smoke at all and the plug is perfectly dry). All the possible causes that the guys told me to check, including the crank seal - which I also feel it is the most probable one, should have effect on both cylinders. Right?

Not so, there are two carbs, either one or two coils, if one, then it may be a split one and one half is breaking down...

[centaurus]

Well, I checked the gearbox oil today. I don't know which is the correct level, but if the bike is on the kickstand, I reach the gears before the oil, so it's obviously not enough oil. This means it' the gasket between the gearbox and the cranck case.

Now question: can I just unscrew and take off the gearbox cap from the right side of the engine, or I have to take all the engine off the bike and dismantle from the cylinders side? I have some experience with cars, but I haven't worked on a bike before and I don't have anything remotely close to a repair manual, so I'm kinda walking in a dark, feeling my way through.

[jade]

The plugs you wanna run are br9ES's if I remember correctly... you dont want 10's
I had an mc18 and altho I didnt have problems with idling my lower plug would fowl up almost everyday if I wasnt riding hard enough
I would just take that plug out, dip a brush into the fuel tank and give the plug a quick clean - problem solved and replaced the plug,
Also I think with this bike, everytime you arent riding it - you wanna turn the fuel off - I was told by a mechanic that this model had a problem when its on its stand, mixed fuel and oil would seep down into the lower cylinder some how fowling the pluge..

[FilthyLuka]

I reach the gears before the oil, so it's obviously not enough oil.

eeep... get a service manual, shit, ill go and hunt one down for you! never put oil in based on what you can see through the "pour oil in here" hole... im sure theres a dude that did that with his fxr and ended up with white smoke pouring out of both sides of the engine...

ill have a scratch around for a mc18 manual...

and definetly not when its on its kick stand! center stand... wait a sec, nsr's dont have those... hunt down a swing arm race lifety the rear wheel thing... or get a mate to hold the bike up...

[centaurus]

eeep... get a service manual, shit, ill go and hunt one down for you! never put oil in based on what you can see through the "pour oil in here" hole... im sure theres a dude that did that with his fxr and ended up with white smoke pouring out of both sides of the engine...

ill have a scratch around for a mc18 manual...

and definetly not when its on its kick stand! center stand... wait a sec, nsr's dont have those... hunt down a swing arm race lifety the rear wheel thing... or get a mate to hold the bike up...

Bro', if you find me an NSR manual, I'll be eternally grateful. I took off the clutch and the oil seal and now I'm just about to order, by I have a suspicion that the old oil seal was mounted the other way around, but I can't verify my theory with anything.

[FilthyLuka]

very good... ill try hunt down a manual but if i come up dry, im sure someone on here knows how much oil to put in a cunting nsr250 gearbox! Hmm, oil seal around the wrong way... hehe... grab another one. I highly recomment new rings and getting you barrells honed while your playing about with engine internals... your bike will be gratefull for it!

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